Make sure you don't have "Basic Editor" checked under "Message Editor Interface:". I recommend the enhanced editor. Secondly, make sure you aren't using an addon like noscript which could be blocking javascript functions on MPGH. If you are, disable it. Let me know if that helped. @N00B1O2

EDIT: Wait, I'm having the same problem. Looks like MPGH is falling apart after arun's hostile takeover. Once we get Dave back, the problem should be fixed. Until then, just write the markup yourself. That's what I always do anyway. You can use Google to find standard bbcode markup.